Municipal Waste Incineration Fly Ash Research Articles

Co-treating MSWI fly ash in iron ore sintering process: Influence of water-washing and roll forming pretreatment on dioxins emission

Co-treating municipal solid waste incineration fly ash (MSWI-FA) in high-temperature iron ore sintering process is winning great concern. Most of the previous studies were about the co-treatment of raw MSWI-FA (without water washing) in sintering process. Although the content of dioxins in MSWI-FA was reduced, the high chlorine content promoted the secondary synthesis of dioxins and had a negative impact on the quality of sinter. This investigation focused on the emission characteristics and regulation approach of dioxins as co-treating MSWI-FA. The results showed that when MSWI-FA was added without pretreatment, the emission concentration of dioxins in sintering flue gas reached 4.28 ng I-TEQ/Nm³ . After water-washing pretreatment, the chlorine in MSWI-FA was significantly reduced, which inhibited the synthesis of dioxins via de novo reaction. The dioxins decreased significantly to 1.44 ng I-TEQ/Nm³ . Based on the washing pretreatment, the MSWI-FA was further prepared into lumps, which inhibited the dispersion of Cl-containing MSWI-FA particles in mixtures and reduced the active sites of dioxins synthesis, thereby hindering the dioxin synthesis path. The emission concentration of dioxins in sintering flue gas was further reduced from 1.44 ng I-TEQ/Nm³ to 1.15 ng I-TEQ/Nm³ . Adding 0.5% water-washed fly ash lumps had little effect on sintering indexes and dioxins concentration in flue gas. The research results laid a certain foundation for the large-scaly recycling of MSWI-FA.

Removal of heavy metals from fly ash using electrodialysis driven by a bioelectrochemical system: a case study of Pb, Mn, Cu and Cd

ABSTRACT Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to high leachable heavy metals, and incineration leachate belongs to organic wastewater with high biodegradability. Electrodialysis (ED) has shown potential for the removal of heavy metals from fly ash, and bioelectrochemical system (BES) employs biological and electrochemical reactions to generate electricity and remove contaminants from a wide range of substrates. In this study, the ED-BES coupled system was constructed for the co-treatment of fly ash and incineration leachate, where the ED was driven by BES. The treatment effect of fly ash by varying additional voltage, initial pH and liquid-to-solid (L/S) ratio was evaluated. Results showed that the highest removal rates of Pb, Mn, Cu and Cd were 25.43%, 20.13%, 32.14% and 18.87% after 14 days treatment of the coupled system, respectively. These values were obtained under 300 mV of additional voltage, L/S 20 and initial pH3. After the treatment of the coupled system, the fly ash leaching toxicity was lower than the threshold of GB5085.3-2007. The highest energy saving for removed Pb, Mn, Cu and Cd were 6.72, 15.61, 8.99 and 17.46 kWh/kg, respectively. The ED-BES can be considered a cleanliness approach to treating fly ash and incineration leachate simultaneously.

Preparation and characterization of mortar specimens based on municipal solid waste incineration fly ash-activated slag

Municipal solid waste incineration fly ash (MSWIFA) contains a large amount of heavy metals, inhibiting resource utilization. This study used MSWIFA as an alkali activator and ground-granulated blast-furnace slag (GGBS) as a precursor to prepare the MSWIFA GGBS binder. Based on this, used the iron tailing sand instead of natural river sand as fine aggregate prepared mortar specimens by cooperative compression molding. Compressive strength, bulk density, water absorption, and heavy metal leaching tests were conducted and combined with micro XRD, FTIR, and SEM examinations to characterize the mortar specimens. The results show that the optimal MSWIFA: GGBS was 2:8. It was also found that increasing the molding pressure was beneficial to strength development. Compared to the specimens without the application of molding pressure, the 3 d and 28 d strength values increased by 148.6 and 122.2%, respectively, after the application of 35 MPa molding pressure. The reason is that the pressure effect can increase the cohesion of the particles, promote the hydration reaction to proceed, and the hydration products increase to fill the pores, increase the structural compactness and promote strength development. The resource utilization of MSWIFA must be guaranteed not to produce environmental pollution simultaneously. For this reason, the heavy metal leaching test was conducted on 28 d mortar specimens, and the results showed that the leaching rates of Zn, Pb, Cu, Cr, and Ni met the requirements of the Chinese Standard (GB16889-2008). The research results can provide a theoretical basis for the large-scale recycling of MSWIFA.

Numerical simulation on the deposition characteristics of MSWI fly ash particles in a cyclone furnace

In melting municipal solid waste incineration (MSWI) fly ash by cyclone furnace, the deposition characteristics of particles affect the slag flow and the secondary MSWI fly ash formation. In this study, the composition mechanism based on critical viscosity is selected as the particle deposition model to predict the deposition and rebound of particles on the furnace wall. The Riboud model with an accurate viscosity prediction performance is selected, then the particle deposition model is integrated into a commercial computational fluid dynamics (CFD) solver through the user-defined function (UDF) to realize the coupling of particle motion and deposition process. The results show that under the same case, the deposition rate decreases obviously with the increase of MSWI fly ash particle size. And the escape rate reaches a maximum at particle size 120 μm. Controlling the particle size of fly ash particles within 60 μm can effectively reduce the generation of secondary MSWI fly ash. During the forward movement of the fly ash inlet position, the escape of MSWI fly ash particles with large particle sizes has been significantly weakened. This measure not only lowers the post-treatment cost but also dramatically reduces the pretreatment step of MSWI fly ash before the melting and solidification process. In addition, the deposition rate and quality will reach the maximum values, respectively, along with gradually increasing MSWI fly ash input flow. Overall, this study has the guiding significance for reducing the pretreatment steps and post-treatment costs of MSWI fly ash by melting in the cyclone furnace.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS2 nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS2 nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS2 in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

The toxic leaching behavior of MSWI fly ash made green and non-sintered lightweight aggregates

With the rapid development of urbanization and the economy, the amount of municipal solid waste incineration fly ash (MSWI fly ash) dramatically increases and stacks up. Declining the leaching concentration of hazardous heavy metals in municipal solid waste incineration fly ash and enlarging the application range in wastewater and biosorption of non-sintered LWAs have always got more attention from more and more researchers. Green and non-sintered LWAs were prepared by using the waste solids (MSWI fly ash and coal fly ash) as raw materials through autoclave technology. In the meantime, the effect of severe leaching environment (pH = 1, 3, 5 and 7) on the stabilization of heavy metals in the LWAs with MSWI fly ash and extra heavy metals were systematically investigated by means of Inductively Coupled Plasma Optical Emission Spectrometer, X-ray diffraction, Fourier Transform Infrared Spectrometer, X-ray photoelectron spectra and Scanning electron microscope. The results revealed that the heavy metals are well immobilized in the LWA matrix through physical encapsulation and adsorption by hydration products (C-S-H). The leaching rate (LR) and cumulative leaching rate (CLR) of heavy metals, phase compositions and chemical structures in LWAs with heavy metals at pH of 1 are significantly changed, but the cumulative leaching rate of Pb2+ is lower than that of Zn2+ and Cu2+. The structure of hydration products in the matrix will be broken and reformed to gypsum under an acid environment (pH = 1). The leaching rate and cumulative leaching rate of heavy metals in LWAs with heavy metals under various leaching environments are much lower when the pH is above 1, which could meet the leaching requirement. This research could provide theoretical support for the application of non-sintered and municipal solid waste incineration fly ash based LWAs in concrete.

Thermal treatment of municipal solid waste incineration fly ash and nanofiltration membrane concentrate co-processing: Speciation of chromium and its leachability

The thermal treatment of municipal solid waste incineration fly ash (MSWI FA) has raised serious concerns due to the increasing leaching concentration of Cr, and Cl severely limits the reuse and utilization of MSWI FA. A nanofiltration membrane concentrate (NF-MC) is utilized in this study to leach the MSWI FA to remove Cl and the fate of Cr in the leaching MSWI FA by NF-MC (L-MSWI FA) is investigated. The results showed that Cl in the MSWI FA was effectively removed at a removal rate greater than 95%. After the thermal treatment of the proportion of the MSWI FA based on the L-MSWI FA (P-MSWI FA), it was revealed that Cr primarily as Cr2O3 hexagonally shaped flake-like crystallites, was oxidated first to Cr(VI), and the leaching concentration reached the maximum (1.17±0.05 mg/L) at 800°C. Cr(VI) was then reduced, and the chemical valence of Cr between Cr(III) and Cr(VI) confirmed that the leachability of the Cr-containing materials rose after the thermal treatment. In addition, it was believed that Cr(VI) was reduced when the temperature was greater than 1000°C. The results of this study provide theoretical guidance for controlling the enhancement of Cr leachability during the thermal treatment process.

Influence of leaching agents on the melting behavior of MSWI fly ash and its variation mechanism

In this paper, a new technology was proposed to substantially decrease the high cost of plasma melting of municipal solid waste incineration (MSWI) fly ash(FA) and the mechanism was studied. MSWI FA was leached with water, ammonium chloride (NH4Cl) solution and hydrochloric acid (HCl) solution. X-ray diffraction(XRD) and X-ray fluorescence(XRF) results indicate that soluble chloride, soluble chloride plus Ca (OH)2, and soluble chloride, Ca (OH)2 plus CaCO3 from the ash, were removed, respectively. Their flowing temperatures (FT) were decreased from 1545 °C to 1529 °C,1380 °C and 1197 °C, which is well related to their slag contents calculated with FactSage 7.3. Through FactSage simulation of mineral composition during heating process and the ternary phase diagram of SiO2–CaO–Al2O3, the influence of leaching agents can be attributed to the content of CaO. With the decrease of CaO content, the chemical compositions of the ash move from high liquidus temperature area to low liquidus temperature area. Acid-leaching technology can substantially decrease the cost of plasma melting of MSWI FA by both greatly decreasing the melting temperature and the amount of ash to be molten.

Footprints in compositions, PCDD/Fs and heavy metals in medical waste fly ash: Large-scale evidence from 17 medical waste thermochemical disposal facilities across China.

Chemical compositions, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) profiles and heavy metals (HMs) leachability of medical waste fly ash (MWFA) from 17 thermochemical treatment facilities in eight Chinese provinces were first investigated. Large-scale and extended monitoring revealed high chloride and Zn contents and similar PCDD/Fs congener profiles in MWFA. Particularly, the PCDD/Fs and HMs concentrations implied greater toxicity than that observed for municipal solid waste incinerator fly ash (MSWIFA). The maximum international toxic equivalent value of PCDD/Fs in MWFA was 40 times that of MSWIFA, and the leaching concentrations of Zn and Hg were 15 and 4 times those of MSWIFA, respectively. Notably, MWFA characteristics suggest the possibility of recycling and sustainable disposal solutions owing to the high Cl and Zn content with good recovery instead of landfill disposal. Similarities in chemical composition, PCDD/Fs homolog distribution, and water-solubility of chloride salts allows co-processing of MWFA and MSWIFA via water-washing detoxification and thermal treatment, such as that used in cement kilns. This study supplements existing literature on the characteristics and risk management of MWFA.

Mechanochemical treatment with red mud added for heavy metals solidification in municipal solid waste incineration fly ash

The effective stabilization of heavy metals municipal solid waste incineration fly ash (FA) is very important for the disposal of FA, due to that heavy metals leaching from FA will induce environmental risks to a content. In this study, Red mud (RM) was used as an additive for the stabilization of heavy metals in FA during the mechanochemical process. The results demonstrated that the addition of RM significantly reduce the leaching of Pb, Cr and Zn from FA. In the conditions of 30 wt% of red mud, 0.1 g L−1 of solid-to-liquid ratio and 24 h of ball-milling time, the leaching concentration of Pb, Cr and Zn decreased by 99%, 81.18% and 100%, respectively. Meanwhile, the residue fraction of Pb, Cr and Zn increased, part of the reducible Cr is changed into acid-soluble fraction of Cr due to oxidation. Moreover, FA was broken into small particles and then agglomerated into larger ones after mechanochemical treatment. The main reasons accounting for the solidification of heavy metals were ascribed to the precipitation and sealing by the fine particles, capture by new phases, dissolution and elution of soluble salt. RM play a key role in forming new phases (include hydrocalumite, andradite and aluminosilicate minerals) which in favor of solidification of heavy metals. This work provides a good method for the effective heavy metals stabilization in FA and presents a new sight into the reuse of RM.

Performance of Asphalt Mastic and Asphalt Mixture with Harmless Municipal Solid Waste Incineration Fly Ash

In this paper, harmless municipal solid waste incineration fly ash (H-MSWIFA) was used to replace part of the mineral powder in asphalt mastic prepared with different ratios of filler to asphalt (F/A). Cone penetration (CPT), rotational viscosity, low-temperature bending, and full section fracture energy(FSFET) tests on the prepared H-MSWIFA asphalt mastic were carried out to evaluate the viscosity at room temperature, viscosity at high temperature, tensile property at low temperature, and crack resistance at room temperature of the asphalt mastic with different F/A and different H-MSWIFA content. An asphalt concrete mixture with a nominal maximum particle size of 13 mm (AC-13) with different F/A and H-MSWIFA replacement ratios was prepared. The effects of F/A and H-MSWIFA content on the high-temperature stability, water stability, and low-temperature cracking resistance of the asphalt mixture were studied. The results showed that the shear strength and viscosity of the asphalt mastic increased after H-MSWIFA replaced part of the mineral powder; and the greater the F/A, the greater the shear strength and viscosity of the asphalt mastic. H-MSWIFA can greatly improve the viscosity of asphalt mastic at high temperatures, and with the increase in H-MSWIFA content, the improvement effect becomes more obvious. The high-temperature stability of the asphalt mixture is not related to H-MSWIFA content but mainly depends on the F/A. Both the F/A and the H-MSWIFA replacement ratio can significantly affect the water stability of the asphalt mixture, specifically, the water stability reaches the best value when the F/A is around 1.0, and the addition of H-MSWIFA harms water stability. Both the F/A and the H-MSWIFA replacement ratio can significantly affect the low-temperature cracking resistance of the asphalt mixture. The higher the F/A, the worse the low-temperature crack resistance. At the same time, the addition of H-MSWIFA harms low-temperature cracking resistance. From the point of view of water stability and low-temperature crack resistance of the asphalt mixture, the H-MSWIFA replacement ratio should not be too high.

Study on preparation of glass-ceramics from municipal solid waste incineration (MSWI) fly ash and chromium slag

In order to realize the harmless treatment of municipal solid waste incineration (MSWI) fly ash and chromium slag, the CaO–SiO2–Al2O3 glass-ceramics were successfully prepared by the one-step method using a mixture of lead-zinc tailings and coal gangue as a flux. The results showed that the mixture successfully reduced the melting temperature of MSWI fly ash with a maximum blending ratio of 70% at 1450 °C, and realized the co-sintering of chromium slag and the base glass of MSWI fly ash. In addition, according to the analysis results of XRD, SEM, and EDS, combined with heavy metal leaching data measured by the TCLP method, diopside ferrous crystals exerted a better solidification effect on Zn and Cd than did gehlenite crystals. Uvarovite crystals exhibited an effective solidification effect on Cr owing to the participation of Cr in its formation, and the toxicity assessment of heavy metals in all samples satisfied the demand of the EPA and the CN GB 5058.3. This work provides a consult for the low-cost, green and efficient treatment of chromium slag, MSWI fly ash, coal gangue, and lead-zinc tailings.

Exposure levels of PCDD/Fs from co-landfill scenario with MSW and stabilized fly ash during hydrolysis-acidogenesis

The rapid generation of municipal solid waste incineration fly ash has brought a huge burden to the management of landfill. After stabilization treatment, most of stabilized fly ash was landfilled separately, whereas the remaining stabilized fly ash may be landfilled together with refuse. PCDD/Fs from stabilized fly ash in a co-landfill scenario can be released into the environment and cause potential risks. In this study, the leaching behavior and related influencing factors of PCDD/Fs from stabilized fly ash were investigated during the co-landfilling of stabilized fly ash and municipal solid waste using different co-landfill modes (layered co-landfill and mixed co-landfill). The results showed that the leaching concentration of PCDD/Fs in the layered co-landfill was significantly higher than that in the mixed co-landfill. The highest concentration of mass and I-TEQ for column L were 104.9 pg/L and 3.2 pg/L, which were 43.9 pg/L and 1.6 pg/L for column M. High leaching period was 0–56 days for the layered co-landfill, whereas which was 0–28 days for the mixed co-landfill. Distribution results of PCDD/Fs mass concentration and I-TEQ concentration showed that H7CDD/Fs and O8CDD/Fs were the main homologues in the leachate, while H6CDF was dominant contributor to the I-TEQ concentration. The correlation analysis results showed that pH and EC affect the leaching behavior of PCDD/Fs by changing the structure of dissolved organic matter, and the leaching concentration of PCDD/Fs decreased with a decrease of the molecular weight and the degree of humification of dissolved organic matter. The change of protein-related functional groups significantly affected the leaching concentration of PCDD/Fs. Although the mixed co-landfill has lower environmental risk to the landfill, which still posed a threat to the eco-environment and human health around the landfill. It is essential to avoid co-landfill of stabilized fly ash and refuse, especially massive stabilized FA should be prohibited to enter the MSW landfill simultaneously.

Co-treatment of municipal solid waste incineration fly ash (MSWI FA) and municipal sludge: A innovative method to improve sludge dewatering with fly ash dechlorination

The complexity of municipal sludge dewatering is a bottleneck problem limiting resource utilization. In this paper, adding municipal solid waste incineration fly ash (MSWI FA) to municipal sludge for enhanced dewatering was applied, while the chlorine salt in MSWI FA was simultaneously removed using water in municipal sludge. The effects of different dosages and chemical components of MSWI FA on municipal sludge dewatering, and the removal effect of municipal sludge washing on Cl element were investigated. The results showed that the municipal sludge's specific resistance to filtration after co-treatment was significantly reduced, and more hydrophobic channels were formed in the vacuum suction filtration of the treated municipal sludge, conducive to efficient water removal. The moisture content of municipal sludge was reduced from 96.0% to 48.3%, and the moisture reduction rate increased from 17.7% to 32.1%. The chemical composition of MSWI FA could effectively promote the dewatering of municipal sludge, among which CaO was the best, followed by CaCl2 and NaCl, and KCl was the worst. Simultaneously, the municipal sludge showed a good effect on removing Cl from MSWI FA. The minimum Cl content in the mixture after Co-treatment is 1.5%. These results could provide a new way to dispose of MSWI FA and municipal sludge.

Study on the reduction of chlorine and heavy metals in municipal solid waste incineration fly ash by organic acid and microwave treatment and the variation of environmental risk of heavy metals

Municipal solid waste incineration (MSWI) fly ash usually needs to undergo dechlorination or heavy metal stabilization pretreatment for further treatment, recycling or disposal. In this paper, the removal effect of chlorine in fly ash by water washing, lactic acid, citric acid and microwave treatment was studied, and XANES was used to analyze chlorine chemical form in fly ash. In addition, the heavy metals in fly ash were also checked. The results indicated that double washing and triple washing could remove 88.0 % and 95.5 % of chlorine from fly ash respectively. The “double water washing + microwave/organic acid” could remove about 96.6 % of chlorine, and 42.9 % and 47.2 % of insoluble chloride respectively. The microwave treatment could maximize the stabilization of heavy metals with a BI value of 39.1 %, 0.11 %, 1.65 %, 15.4 % and 3.98 % for Cd, Cr, Cu, Pb and Zn. The elution of heavy metals by citric acid was obvious. “Double water washing + citric acid” removed 87.0 % of Cd, 17.2 % of Cr, 11.9 % of Cu, 39.6 % of Pb and 43.6 % of Zn, but the environmental risk of Cu and Cr increased about 2–3 % after the treatment. The results of this study provide guidance for the pretreatment of fly ash before resource utilization.

Preparation of High-strength ceramsite from municipal solid waste incineration fly ash and clay based on CaO-SiO2-Al2O3 system

With the increasing production of incineration fly ash (FA), its disposal has attracted more and more attention. Based on the transformation behavior of the FA/clay system during the sintering process, the feasibility of preparing high-strength ceramics from FA/clay was evaluated from the theoretical analysis and experimental verification perspective. The theoretical analysis showed that mixing FA and clay can reduce the liquid formation temperature, promoting the sintering process. Meanwhile, according to the CaO-SiO2-Al2O3 phase diagram, by controlling the addition of FA of 40 wt%, the potential balanced phases of the FA/clay system can be transformed into anorthite (CaAl2Si2O8), which is a typical ceramsite forming phase. The X-ray diffraction analysis confirmed that anorthite was the dominant phase in the sintered FA/clay sample. The experimental verification results presented that under the addition of 40 wt% FA, the sintering temperature of 1200 °C, and the holding time of 20 min, the obtained ceramsite with extremely excellent strength performance and heavy metal stability can meet the quality requirements of lightweight aggregates. This study can provide a reference for the resource utilization of FA and related hazardous wastes.

Accelerated carbonation of ball-milling modified MSWI fly ash: Migration and stabilization of heavy metals

Mechanical ball-milling is an effective technique to reduce particle size, increase lattice defects, and enhance the activity of materials. After mechanical ball-milling modification, an accelerated carbonation technology of municipal solid waste incineration fly ash (FA) was proposed. The effects of ball-milling on carbonation efficiency, heavy metals stabilization, and heavy metals leaching characteristics were investigated. The results showed that the initial carbonation efficiency of ball-milled FA (MFA) was higher than that of the original FA (OFA) because of the in-situ carbonation reaction and the stability of Pb, Cu, and Cd in MFA was improved. The carbonation reaction of MFA was conducted thoroughly by the elevated ionic strength and mass transfer efficiency. The surface of carbonated OFA (COFA) and carbonated MFA (CMFA) stacked calcium carbonation in loose strips and compact spherical respectively, relating to the initial morphology. The dechlorination of CMFA was superior to COFA because the more in-depth carbonation eluted the chlorine from Friedel’s salt. The leaching concentrations of heavy metals in CMFA were lower than those in COFA, especially the immobilization efficiency of Pb and Zn reached 99.8 % and 98.5 %, respectively, contributed by the conversion of the Pb and Zn from ionic hydroxides to stable carbonates. Due to the low acid neutralization capacity of CMFA, when the pH dropped from 7 to 5, the heavy metals carbonate chemical precipitation dissolved, and the effect of calcium carbonation on heavy metals wrapping and adsorption disappeared, therefore the subsequent disposal of CMFA should avoid an acidic environment.

Improvement on freeze-thaw durability of municipal solid waste incineration fly ash-based autoclaved wall blocks by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings

The envelope structures hardly have the service life up to the design life in severe cold area. Polymer/nano-materials composite coatings are used to enhance the freeze-thaw durability of wall materials. Municipal solid waste incineration fly ash and fly ash were used to fabricate solid wastes-based autoclaved wall blocks (SW-AWBs) with hydrothermal synthesis method. Nano-Al2O3 and graphene nanoplatelets were modified by the coupling agent and used to prepare composite coatings with triethoxy(octyl)silane. Effect of different coatings on the durability of SW-AWBs was compared and discussed. The results showed that the specimens surface changed from hydrophilic to hydrophobic after treated by composite coatings. Meanwhile, the capillary absorption coefficient of SW-AWBs decreased by 57.3%–78.8% and 92.4%–94.1% after treated by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings, respectively. Under 15 freeze-thaw cycles, the mass loss of SW-AWBs dropped by 61.9% and 69.4%, the strength loss reduced by 70.5% and 79.4% after treated by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings, respectively. Overall, triethoxy(octyl)silane/graphene nanoplatelets had a superior effect on improving the freeze-thaw durability of SW-AWBs than triethoxy(octyl)silane/nano-Al2O3.

Solidification and stabilization of Pb–Zn mine tailing with municipal solid waste incineration fly ash and ground granulated blast-furnace slag for unfired brick fabrication

The mismanaged and abandoned mine tailings are an important source of heavy metal pollution in the mining regions, and there is a significant need to develop technically, environmentally, and economically feasible and sustainable solutions to manage them. This study explored the solidification and stabilization of the tailing from an abandoned Pb–Zn mine using municipal solid waste incineration fly ash (MSWIFA) blended with ground granulated blast-furnace slag (GGBFS) for fabricating unfired bricks, and systematically characterized the products’ mechanical and environmental performance. Various hydration products, such as ettringite, portlandite, and hydrotalcite, were formed in the unfired bricks in the solidification and stabilization process, which enhance the physical strength of unfired bricks and help immobilize the heavy metals. Slaking treatment of MSWIFA significantly increased the mechanical strength, reduced the water absorption, and improved the durability of unfired bricks, with the product prepared from MSWIFA with 7-day slaking exhibiting the highest unconfined compressive strength (12.3 MPa) after 56 days of curing. The concentrations of As (0.35–1.49 μg/L), Cd (0.35–0.70 μg/L), Cr (1.38–9.40 μg/L), Cu (2.28–5.87 μg/L), Ni (0.16–2.24 μg/L), Pb (0.16–59.80 μg/L), and Zn (1.60–10.80 μg/L) in the leachates of unfired bricks were below the relevant regulatory limits for surface water and groundwater. Converting the mine tailing (with MSWIFA and GGBFS) to different types of unfired bricks could yield economic payback in the range of 283.7–306.5 Yuan per ton. Replacing cement with MSWIFA blended with GGBFS in the solidification and stabilization treatment could save about 0.15 ton of cement per ton of mine tailing disposed, which avoids significant energy use and carbon dioxide emissions. These findings demonstrate that utilization of mine tailings and industrial wastes to fabricate unfired bricks is a promising way of reusing such wastes and controlling the associated pollution, which also brings significant economic benefit and improves environmental sustainability.

Environmental filling materials based on phosphogypsum powder with municipal solid waste incineration ash

A new building filling materials (NBFM) using phosphogypsum and municipal solid waste incineration (MSWI) fly ash is prepared in this paper. The effects of MSWI fly ash dosage and MSWI fly ash water washing pretreatment on mechanical properties, setting time, metal leaching, hydration products and microstructure of NBFM are analyzed by a range of experimental studies. The results indicate that the mechanical properties, setting time and the density of micro interface of NBFM are optimal when the MSWI fly ash dosage is 3%. The mechanical properties of NBFM rise and the condensation time and leaching concentration of heavy metals decline after washing the MSWI fly ash. With the increase of the curing age, the metal element leaching of NBFM decreases, and when the curing age is 7 days, the solidification effect of NBFM on most metal elements meets the standard of Chinese code (GB5085.3-2007). The feasibility of MSWI fly ash and phosphogypsum as filling materials for building engineering is verified, and the change of macroscopic properties of NBFM is explained as well.